Axial piston pump having fixed slant cam plate for causing reciprocation of pistons

Abstract

An axial piston pump, for pumping an operating oil in a hydraulic system, comprises a rotary cylinder block having a plurality of cylinder bores formed therein and disposed at regular intervals around a rotational axis thereof. Each bore is opened at a bottom thereof through a hole formed in an end wall of the cylinder block, a plurality of pistons being slidably received in the bores, respectively. Further, the pump comprises a fixed slant cam plate engaged with the pistons during a rotation of the block, for causing a reciprocation of the pistons within the cylinder bores, and a fixed valve plate having a suction port and a discharge port. The block end wall is resiliently pressed against the valve plate so that the holes of the bores are operatively connected with the suction and discharge ports of the valve plate during the rotation of the block. The valve plate has an annular seal land formed thereon and surrounding the ports, to thereby form an annular oil groove around the annular seal land, and a plurality of bearing lands formed at regularly spaced intervals along a periphery of the valve plate member, to thus form a radial oil passage between two adjacent bearing lands. The radial oil passage is at least partially defined by a cylindrical surface or sloped surface so that a penetration of the operating oil from the radial oil passage into a fine space between the bearing lands and the cylinder block end wall.

We claim: 
     
       1. An axial piston pump for pumping an operating oil through a hydraulic system, said pump comprising: a rotary cylinder block having a plurality of cylinder bores formed therein and disposed at regular intervals around a rotational axis thereof, each of said cylinder bores being opened at a bottom thereof through a hole formed in an end wall of said rotary cylinder block;   a plurality of pistons slidably received in said cylinder bores, respectively;   a slant cam plate member engaged with said pistons during rotation of said rotary cylinder block, for causing reciprocation of said pistons within the cylinder bores thereof; and   a fixed valve plate member having a suction port and a discharge port formed therethrough, said end wall of said rotary cylinder block being resiliently pressed against said valve plate member so that said holes of said cylinder bores are operatively connected with said suction and discharge ports of said valve plate member during rotation of said rotary cylinder block, whereby the operating oil is sucked up into each of said cylinder bores in sequence through said suction port of said valve plate member and the corresponding hole of the cylinder bore, and is then discharged from each of said cylinder bores in sequence through said corresponding hole of the cylinder bore and said discharge port of said valve plate member,   wherein said valve plate member is provided with an annular seal land formed thereon surrounding said suction and discharge ports with an annular groove around said annular seal land, and a plurality of bearing lands are formed at regularly spaced intervals along a periphery of said valve plate member with a radial groove between every two adjacent bearing lands; said annular groove and said radial grooves being in communication and serving as a guide passage for operating oil leaked from between said annular seal land and said end wall of said rotary cylinder block, and said radial grooves are each at least partially defined by a cylindrical surface extending from a radial side edge of the corresponding radial groove, which side edge is defined as a trailing side edge with respect to a rotating surface of said end wall of said rotary cylinder block, to a bottom of said radial groove, whereby penetration of said operating oil between said bearing lands and said end wall of said rotary cylinder block is facilitated.   
     
     
       2. An axial piston pump as set forth in claim 1, wherein, at the boundary between said cylindrical surface of each radial groove and the bearing surface of the adjacent bearing land, said cylindrical surface forms an angle of about 10 to about 30 degrees to a plane extended from said bearing surface of said bearing land. 
     
     
       3. An axial piston pump as set forth in claim 1, wherein said radial grooves are each defined by a respective cylindrical surface extending from said corresponding radial side edge to an opposite radial side edge. 
     
     
       4. An axial piston pump as set forth in claim 3, wherein, at the boundary between said cylindrical surface of each radial groove and the bearing surface of the adjacent bearing land, said cylindrical surface forms an angle of about 10 to about 30 degrees to a plane extended from said bearing surface of said bearing land. 
     
     
       5. An axial piston pump for pumping an operating oil through a hydraulic system, said pump comprising: a rotary cylinder block having a plurality of cylinder bores formed therein and disposed at regular intervals around a rotational axis thereof, each of said cylinder bores being opened at a bottom thereof through a hole formed in an end wall of said rotary cylinder block;   a plurality of pistons slidably received in said cylinder bores, respectively;   a slant cam plate member engaged with said pistons during rotation of said rotary cylinder block, for causing reciprocation of said pistons within the cylinder bores thereof; and   a fixed valve plate member having a suction port and a discharge port formed therethrough, said end wall of said cylinder block being resiliently pressed against said valve plate member so that said holes of said cylinder bores are operatively connected with said suction and discharge ports of said valve plate member during rotation of said cylinder block, whereby the operating oil is sucked up into each of said cylinder bores in sequence through said suction port of said valve plate member and the corresponding hole of the cylinder bore, and is then discharged from each of said cylinder bores in sequence through said corresponding hole of the cylinder bore and said discharge port of said valve plate member,   wherein said valve plate member is provided with an annular seal land formed thereon surrounding said suction and discharge ports with an annular groove around said annular seal land, and a plurality of bearing lands are formed at regularly spaced intervals along a periphery of said valve plate member with a radial groove between every two adjacent bearing lands; said annular groove and said radial grooves being in communication and serving as a guide passage for operating oil leaked from between said annular seal land and said end wall of said rotary cylinder block, and said radial grooves are each defined by a V-shaped cross-sectional surface extending between two side edges thereof, whereby penetration of said operating oil between said bearing lands and said end wall of said cylinder block is facilitated.   
     
     
       6. An axial piston pump as set forth in claim 5, wherein, the slope of the V-shaped cross-sectional surface of each radial groove forms an angle of about 10 to about 30 degrees to a plane extended from said bearing surface of said bearing land. 
     
     
       7. An axial piston pump for pumping an operating oil through a hydraulic system, said pump comprising: a rotary cylinder block having a plurality of cylinder bores formed therein and disposed at regular intervals around a rotational axis thereof, each of said cylinder bores being opened at a bottom thereof through a hole formed in an end wall of said cylinder block;   a plurality of pistons slidably received in said cylinder bores, respectively;   a slant cam plate member engaged with said pistons during rotation of said rotary cylinder block, for causing reciprocation of said pistons within the cylinder bores thereof; and   a fixed valve plate member having a suction port and a discharge port formed therethrough, said end wall of said cylinder block being resiliently pressed against said valve plate member so that said holes of said cylinder bores are operatively connected with said suction and discharge ports of said valve plate member during rotation of said cylinder block, whereby the operating oil is sucked up into each of said cylinder bores in sequence through said suction port of said valve plate member and the corresponding hole of the cylinder bore, and is then discharged from each of said cylinder bores in sequence through said corresponding hole of the cylinder bore and said discharge port of said valve plate member,   wherein said valve plate member is provided with an annular seal land formed thereon surrounding said suction and discharge ports with an annular groove around said annular seal land, and a plurality of bearing lands are formed at regularly spaced intervals along a periphery of said valve plate member with a radial groove between every two adjacent bearing lands; said annular groove and said radial grooves being in communication and serving at a guide passage for operating oil leaked from between said annular seal land and said end wall of said rotary cylinder block, and said radial grooves are each at least partially defined by a sloped surface extending from a radial side edge of the corresponding radial groove, which side edge is defined as a trailing side edge with respect to a rotating surface of said end wall of said cylinder block, to a bottom of said radial groove, whereby penetration of said operating oil between said bearing lands and said end wall of said cylinder block is facilitated.   
     
     
       8. An axial piston pump as set forth in claim 7, wherein, the sloped surface of said radial groove forms an angle of about 10 to about 30 degrees to a plane extended from the bearing surface of said bearing land.